Lovely Hidden Paintings Adorned the Edges of Historic Books

I bet that there's a certain constancy in the volume of higher end quality books (with some growth given printing tech, etc.) and that it's the bottom end that really has exploded since that side is the and more widely accessible.

Naturally, that would give the appearance of decline, when really it's just the more well to do that care that spend on such things... which would be the same as it's always been.